1. Field
The present invention relates generally to data communication, and more specifically to techniques for detecting and demodulating data transmissions in wireless communication systems.
2. Background
In a wireless communication system, data to be transmitted is typically processed (e.g., coded and modulated) and then upconverted onto a radio frequency (RF) carrier signal to generate an RF modulated signal that is more suitable for transmission over a wireless channel. The RF modulated signal is then transmitted from a transmitter and may reach a receiver via a number of propagation paths in the wireless channel. The characteristics of the propagation paths typically vary over time due to a number of factors such as, for example, fading, multipath, and external interference. Consequently, the RF modulated signal may experience different channel conditions (e.g., different fading and multipath effects) and may be associated with different complex gains across the operating bandwidth of the system.
To achieve high performance, a pilot (i.e., a reference signal) is often transmitted by the transmitter to assist the receiver in performing a number of functions. The pilot is typically generated based on known symbols and processed in a known manner. The pilot may be used by the receiver for channel estimation, timing and frequency acquisition, coherent demodulation, and so on
It is often desirable or necessary to detect for the presence of data transmissions in a received signal. The detection for data transmissions is normally achieved by processing the pilot for each data transmission hypothesized to have been received. If the energy of the pilot is greater than a particular threshold, then the hypothesized data transmission is further processed (e.g., demodulated and decoded). An error detection code, such as a cyclic redundancy check (CRC), is then typically relied upon to determine whether the data transmission was decoded correctly or in error.
In some wireless communication systems, detection based on the pilot alone is not sufficient. This may be the case, for example, when operating at a low received signal-to-noise ratio (SNR). Moreover, an error detection code may not be available for use to verify the correctness of the received data transmission.
There is therefore a need in the art for techniques to detect and demodulate data transmissions in such wireless communication systems.